While larger laser technology can provide a laser source with a line-width of a few Hertz (Hz), the large physical size and high power consumption of larger laser systems make these systems unacceptable for many commercial applications, such as laser gyroscopes, atomic clocks, and distributed fiber optical sensing.
While some laser technology employs micro-cavities as wavelength selection filters to reduce the laser line-width, the line-width of many micro-cavities is quite large due to large free spectral range (FSR) of the micro-cavities.